Tube connecting elements of this kind manufactured of plastic, which are also called fittings, consist generally of polypropylene and if they are used in the sanitary or heating area and thus for instance for the transport of hot water, they have to comply with the regulations of admittance defined by the national authority DVGW. These regulations prescribe that at temperature of 95.degree. C. and under pressure of 18 bar the life time should be 1000 hours, considering the fact, however, that such a kind of tube connectors are only admitted for a pressure of 8,5 bar and a temperature of 70.degree. C.
It has now be found out that the resistance and life time of such tube connecting elements of polypropylene under operation conditions corresponding to the stated admitted values, are far below 1000 hours. Already after 100 hours the occuring tensions within the material cause deformations which can at first be realized by the fact that the material becomes discolored, which color changes extend in a circular arch like manner as diagrammatically shown in FIG. 1 of the drawings by dotted lines with the consequence that relatively quickly cracks and breaks of the material occur in the discolored areas.
Similar appearances of deformation or fatigue of material in connection with deformation or cracks are also observed in angularly formed tube connecting elements and have therefore been subject of numerous tests and basic considerations having the purpose to delete these drawbacks and to increase the resistance or life time, respectively, of such tube elements under comparably high inside pressures and inside temperatures.
The above mentiond purpose corresponds also to the main object underlying the invention, i.e. to overcome the above stated drawbacks in order to improve the quality of this kind of tube connecting elements.
In this connection it is an especial object to be solved to increase the resistance and the life time of this kind of tube connecting element if they are used under high inside pressure and high inside temperatures so that sanitary equipments and heating equipments including this kind of tube connecting elements operate more reliable and need relatively low cost for maintenance and repair.
These and other objects are solved according to the invention by the fact that the sleeve element is provided with a bore connecting the two bores of the connecting sleeve elements, which bore is with respect to the center line of the two bores provided with a center line offset in the direction to the outer wall of the T-configured tube connecting element located opposite or to the perpendicularly extending bore, which connecting bore is provided with a diameter B smaller than the diameters A1, A2 of the bores of the connecting sleeve element, and which is separated from the perpendicularly extending bore by its bottom wall having a thickness C corresponding generally to the wall thickness D1 of the connecting sleeve elements and being joined with the perpendicularly extending bore by a bore, the cross section thereof being in general smaller by the wall thickness D1 of the connecting sleeve element than the cross section of the perpendicularly extending bore.
Characterizing for this structural configuration of the tube connecting elements is not only the fact that these elements completely comply with the test conditions, i.e. the use of polypropylene as material under an operational temperature of 95.degree. C. and an operational pressure of 18 bar over 1000 hours without such a strong deformation that the elements burst, but also the fact that those test conditions are reached withoug essential change of the weight of the connecting element and without a structural change of its configuration as well as without essential change of the throughput. This means no increase of manufacturing cost with respect to the former conditions and also no change of the connecting conditions, as plastic tubes already used can be welded into the new tube connecting elements without raising problems.
According to an advantageous embodiment of the subject invention the connecting bore between the perpendicularly extending bore and the sleeve body bore is provided with an elliptical cross section in which the greater main axis of the ellipse extends rectangularly to the parallel longitudinal axis of the connecting sleeve bores and the sleeve body bores. In this connection the smallest diameter of the connecting bore which in case of an elliptic cross section of that bore corresponds to the length of the small main axis of the ellipse and which extends parallel to the longitudinal axis of the bores, can be in general 2/3 of the diameter of the connecting sleeve bores and the diameter of that bore of the sleeve body extending perpendicularly to the connecting sleeve bores.
Moreover, it is advantageous to configure the tube connecting element such that the sleeve body bore extending eccentrically to the connecting sleeve bores and joining them is provided with a diameter corresponding to the inner diameter of the plastic tubes welded into these connecting sleeve bores so that over an essential part of the circumference of the sleeve body bore a smooth transition between the inner wall of the sleeve body bore and the inner wall of the welded in plastic tubes is provided.
It has also been found advantageous to arrange the connecting bore between the perpendicularly extending bore and the sleeve body bore eccentrically to the longitudinal axis of that bore extending perpendicularly to the connecting sleeve bores and moreover to provide the largest diameter of the connecting bore with respect to the diameter of the sleeve body bore such that the connecting bore penetrates the sleeve body bore up to the center line of the connecting sleeve bores.
Moreover, the eccentricity of the sleeve body bore with respect to the two adjacent connecting sleeve bores should advantageously in general correspond to the thickness of the connecting sleeve wall.
According to a further embodiment of the subject invention the tube connecting element is configured as an angeled element provided at the front faces with connecting sleeve elements for welding in plastic tubes and which is characterized therein that the tube arc connecting the two connecting sleeve elements is provided with a wall protrusion located opposite to its inner wall and narrowing the flow through cross section, which protrusion is limited by axial wall portions extending perpendicularly to one another forming with the inside wall portions of the connecting sleeve elements a unit, the construction being such that the protrusion in the direction to the connecting sleeve elements is defined by their bottom up to which the plastic tubes which are to be welded-in can be inserted.
The invention is also, briefly, a tube connecting element of plastic for sanitary and heating purposes in the form of an elbow having two axial bores. The elbow has an outer arc and inner walls diametrically opposed to the each other, and an inner curve on the circumferential inner surface of the outer arc and an outer curve on the circumferential outer surface of the outer arc. Two tube connecting sleeve elements are provided at the ends of the elbow, the connecting sleeve elements each having a bore into which a plastic tube may be welded. The element is characterized in that the elbow joining the two connecting sleeve elements is provided with a protuberance having bottom wall portions extending axially and perpendicularly to one another positioned on the inner wall of the elbow opposite the inner curve and which diminishes the throughflow cross section Q. The inner wall of the tube connecting sleeve elements forms a unitary element with the bottom wall portions. The construction is such that the bottom wall portions of the wall protuberance extend radially inwardly from inner surfaces of the inner wall and is an abutment for the plastic tubes which are to be welded in the connecting sleeve elements. The element is further characterized in that the two axial bores of the elbow are eccentrically arranged with respect to the center lines of the two axial bores of the tube connecting sleeve elements.
Further advantageous embodiments of the invention can be gathered from the sub claims.